Iron producing blast furnace operations



United States Patent 3,231,367 IRON PRODUCING BLAST FURNACE OPERATIONS Julius H. Strassburger, Coraopolis, Pa., Edward J. Ostrowski, Steubenville, Ohio, and James R. Dietz, Weirton, W. Va., assignors to National Steel Corporation, a corporation of Delaware No Drawing. Filed Nov. 24, 1961, Ser. No. 154,820 1 Claim. (Cl. 75-41) The invention is concerned with novel methods for operating blast furnaces utilizing such fuels to replace part or all of conventional blast furnace coke.

In conventional blast furnace practice, iron ore, flux, and coke are introduced in predetermined weighted proportions at the top of the furnace and a blast gas is introduced at the bottom of a furnace through main tuyeres. The coke provides permeability for the ascending gases in the stack, heat for the smelting operation and carbon monoxide for the reduction process.

Coke is one of the most expensive raw materials in the production of iron. For every ton of iron produced, about /4 ton of coke, or more, is required. Depending on the locality, coke accounts for one third to one half, or more, of the total cost of raw materials going into an iron producing blast furnace. Additionally, the supply of high grade coking coals required to produce good coke is limited and diminishing.

One object of the invention is to replace coke economically in the production of iron; another is to improve blast furnace operations while replacing coke with a novel, more plentiful, and more versatile fuel. Some of the improvements which result from replacing coke in accordance with the invention include:

Better operational control comprising smoother furnace operation and more responsive metal analysis control;

A decrease in solution loss (loss of carbon monoxide through the top of the furnace);

More effective utilization of fuel resulting in an increase in fuel efficiency and a decrease in the over-all blast furnace fuel requirements per ton of iron produced; and An increase in the driving rate of the furnace and the iron ore capacity of the furnace causing an increase in the tons of iron produced per unit of time.

A significant contribution of the invention is the adaptability of these and other improvements to existing blast furnace structures.

The invention utilizes a pulverized solid fuel in a liquid carrier medium forming a fuel slurry. Pulverized solid fuels include finely divided coal (anthracite, bituminous, or strip), petroleum coke, char, common coke, or other solid carbonaceous materials. An expensive fuel, blast furnace coke, is supplanted by these less expensive carbonaceous materials. In addition, the liquid carrier medium can contribute to the replacement of coke, as well as control or contribute to important blast furnace reactions, so that the fuel slurry itself has advantages over and above the substitution of a less expensive carbonaceous material for coke.

The method of introducing fuel slurry contributes in a large measure to the advantages of the invention. Historically the first blast furnace fuel, charcoal, was added through the top of the furnace; later coke was substituted for charcoal, the coke still being added through the top of the furnace. Blast furnace fuels have continuously been top added and this has generally, been considered as advantageous since it gave the fuel and other raw materials the opportunity to be heated before reaching the more reactive lower portions of the furnace. In brief, top added fuel has been an innate part of the blast furnace I CC Patented Jan. 25, 1966 art. The invention departs from this practice by introducing a pulverized-solid fuel slurry into the bottom of the furnace, preferably through the main tuyeres. Both the fuel slurry and its method of introduction contribute to the advantages of the invention.

One advantage is better operational control of the blast furnace. Bottom added fuel slurry can be injected when needed and where needed, at the blast furnace raceway. By conventional practice, if additional fuel is required by a blast furnace, coke is introduced at the top of the furnace and a wait of 8 to 12 hours ensues while the added coke descends through the stack to the raceway Where it can be effective in controlling hearth temperature or for other purposes. In contrast is the practice of the invention; when added fuel is needed fuel slurry injection is increased and the furnace receives the added fuel in the raceway immediately. Iron production at the desired analysis can be had within a very short period rather than at the end of the normal 8 to 12 hour wait.

A decrease in solution loss is another advantage resulting from adding fuel slurry through the bottom of the furnace rather than adding the conventional coke through the top of the furnace. The solution loss reaction is endothermic and takes place about midway in the stack. In this reaction, carbon dioxide is reduced by carbon and carbon is oxidized to produce carbon monoxide. Carbon monoxide, an important reducing agent in blast furnace operations, escapes with the top gases because there is little or no opportunity for its use in the stack above the solution loss reaction zone. This reaction is considerably reduced during practice of the invention since coke additions through the top of the furnace are reduced. With less carbon available at the solution loss reaction zone less carbon is consumed by carbon dioxide to produce carbon monoxide which escapes with the top gases. The decrease in solution loss reaction therefore improves fuel utilization efficiency and helps bring about the decrease in overall fuel requirements experienced when following the teachings of the invention.

Fuel introduced in accordance with the invention is utilized more efficiently for other very important reasons. There is more opportunity for this fuel to react with furnace ingredients than that experienced with conventional top added fuels. Heat from this novel fuel is produced where needed, and when needed, and the gaseous reductants produced can react throughout the full height of the furnace. The quantity of gaseous reduce tants from this novel fuel is also considerably increased. Considering only the pulverized solid fuel at this time, coal for example, generates gaseous reductants carbon monoxide and hydrogen. Under conditions present in the furnace, these valuable reducing agents are produced from the volatile matter of the coal. Blast furnace experts generally consider hydrogen as a better reducing agent than carbon monoxide so that the quality as well as the quantity of reducing agents is increased by the practice of the invention over that experienced with conventional practice.

Considering both the pulverized solid fuel and the liquid carrier medium, they combine to increase the production rate of a furnace Without change in furnace dimensions. Increase in production rate is due'to an increase in both driving rate and iron ore-stack volume. The increase in driving rate stems from an increase in the size of the raceway. The raceway is the area opposite the tuyeres where carbon is gasified. As will be explained later, the liquid carrier and the relatively low temperature of both the pulverized solid fuel and the carrier contribute to increasing the cross-sectional area and the volume of the raceway. This increase permits more wind to be blown and increases the driving rate of the furnace. The increase in iron ore capacity of the furnace stems from decreasing the coke in the burden. This permits an increase in the percentage of ore in the burden and the total volume of iron ore in the stack to be treated at any instant is increased. For example, ordinarily coke occupies about 60% by volume of the stack; within the teachings of the invention, the volume occupied by coke in the stack can be reduced to 45% or less. This permits more iron ore to be contained in the stack and the iron ore capacity is thus increased.

In addition to this increase in the volume of ore, the ore is treated more efiiciently during practice of the invention causing an increase in production rate of a furnace and a decrease in fuel requirements per unit ton of iron produced. To analyze this increase in efliciency briefly, solid carbon in the fuel slurry injected at the bottom of the furnace is oxidized opposite the tuyeres making highly heated, highly reactive carbon monoxide available from this source. Additional gaseous reductants are available from volatile matter in the pulverized solid fuel and from the carrier increasing both the quantity and quality of reducing agents in the furnace. Increasing the ore and reducing agents available provides better opportunity for reaction and for faster reaction of furnace materials.

Utilization of fuel slurry provides better control of fuel introduction and distribution in the furnace than was available with conventional methods. Separate valving arrangements can be utilized at each point of injection, for example each tuyere. The slurry itself eliminates many handling problems and quantity control problems and the method of injection permits versatile control of fuel distribution and combustion.

Fuel slurry, as encompassed by the invention, includes a pulverized solid fuel and a liquid carrier medium. Possible carrier mediums for the pulverized solid fuel include water, liquid fuels, or mixtures of water and liquid fuels. Each of the carrier mediums ha certain advantages, and, as will be explained later, furnace operating conditions may at times dictate the use of one or another. One limiting fact-or, regardless of the pulverized solid fuel or the liquid carrier medium, is the permeability of the furnace burden. As the burden moves downwardly through the furnace, iron ore, iron, and slag forming materials take on a spongy or semi-fluid consistency. Permeability of the burden at this zone and in the fusion zone is dependent upon blast furnace coke. It is necessary that incoming gases be able to travel upwardly through the stack, otherwise gas pressure will build up and the furnace will hang. Beneficiating the ore by screening, sintering or pelletizing, can improve permeability to some extent, and may be necessary to handle the increase in driving rate available with the invention, but, within the present status of these arts, it is estimated that approximately 50% of the coke normally used in the furnace will still be re quired to maintain the necessary permeability in and approaching the fusion zone of a blast furnace. However, it is emphasized that this estimated practical limit is based on the status of burden beneficiating art which can be considered as separate from blast furnace operatart. In principle, there is no reason why all blast fur nace fuel requirements cannot be introduced at the tuyere level since carbon is burned chiefly at the tuyere area, there being no important exothermic reactions involving carbon above this area.

Considering carrier mediums, some advantage of water as a carrier medium are its availability and ease in handling. Also solid fuels which contain moisture from atmospheric conditions or as produced need not be dried when preparing the water slurry; for example, wet coal can be utilized as received from the coal washer at the mine and/ or with water due to weather conditions; this eliminates drying equipment and operational cost for such equipment.

Water plays an important role in increasing driving rate of a furnace. Driving rate is a measure of the quantity of carbon gasified by combustion at the tuyere area. The water in the slurry burns coke in accordance with the following reaction: H O+C=CO+H (endothermic) and thereby increases the driving rate of the furnace. Also the water will open up the raceway and permit blowing more wind, making more oxygenavailable to increase the driving rate. The size of the raceway is increased in front of the tuyeres because with water the pulverized solid fuel will require a longer time to carry out the process of combustion. Therefore'combustion will extend a greater distance into the furnace than has been the practice with conventional furnace operation and increase the size of the raceway. This increase in the size of the raceway also increases the amount of furnace burden that is being treated at any instant and this facilitates an increase in the driving rate and contributes to an increase in the production rate of the furnace. Further, with water as the carrier medium an important reductant is added to the blast furnace, hydrogen. The water is also a valuable source of oxygen for increasing the driving rate since this oxygen is added without adding nitrogen as with air.

An operational factor limiting the amount of fuel slurry which can be added when water is the carrier medium is the amount of water that a furnace can handle without running cold. The invention includes teachings for operating a furnace within water addition limitations of a furnace and for extending these limitations of a blast furnace to permit more fuel slurry to be accommoe dated.

A physical limitation relating to the slurry itself is the percentage of pulverized solid fuel that water can accommodate and still maintain the necessary fluidity for easy handling and distribution. With water and pulverized coal, the approximate maximum is by weight coal and 30% by weight water. Solid fuels with differing specific gravities would, of course, affect the weight ratios of solid fuel and water. In the examples to follow, a ratio by weight of two parts coal to one part water has been found to be practical.

Blast gas temperature is one of the most important factors to be considered when injecting fuel slurry. It is of overriding importance when the carrier medium is water. In general, increases in blast gas temperature increase the percentage of total blast furnace fuel requirements that can be injected as fuel slurry. This will be more evident from specific operational data presented below. In these examples, a blast furnace producing approximately 2,000 tons of iron per day, at a 1,200 lb. coke rate, and approximately 75,000 cu. ft. per minute of blast gas is used.

Table I depicts the pounds of pulverized fuel injected per day at various percentages of total fuel requirement, the pounds of water injected per day, the grains of moisture per cu. ft. of blast gas, and the blast gas temperature required.

TABLE #I Pulverized solid fuel-water slurry Grains of Blast Gas Fuel Slurry Injection, Pulverized Water, Moisture Temp. Percent of Total Fuel Solid Fuel, lbs/day per cu ft Required,

Requirement lbs/day of Blast F.

Gas

The data of Table I shows that, with a given blast fur nace, the percentage of total fuel requirements that can be added in the form of a pulverized solid fuel-water slurry is limited by the blast temperature. The maximum blast temperature available, at a given blast furnace installation, is usually determined and limited by furnace auxiliaries, principally the blast furnace stoves. In order to overcome this limitation the invention teaches methods of operation for increasing the maxmum percentage of total fuel requirements that can be added as a watercarrier slurry by utilizing oxygen enrichment of the blast gas. The effect of oxygen enrichment on the percentage of total blast furnace fuel requirements that can be injected at fixed blast gas temperatures is shown in Table 11.

TABLE #H Pulverized solid fuel-water slurry Percentage of Total Fuel Requirement Blast Gas Temperature, Which Can Be Added as Slurry degrees Fahrenheit The method of introducing the fuel slurry and the added oxygen can play an important role in fuel slurry combustion. In a preferred method the fuel slurry is introduced through the main tuyeres. In one embodiment a lance is introduced in the vicinity of the tuyere peep sight and extends longitudinally through the tuyere into the furnace. The lance can also be introduced in angled relationship to the longitudinal axis of the tuyere; the important thing is delivering the fuel slurry contiguous to the point of entry of the blast gas into the combustion zone of the furnace.

In circumstances where the amount of water in the slurry is more than the blast furnace can accommodate, the invention teaches several'methods for handling the water slurry. Those disclosed above include increasing the blast gas temperature, enriching the blast gas with oxygen, or a combination of increasing blasting as temperature and enriching the blast with oxygen. Another method is the substitution of a liquid fuel for Water and/ or the combination of this method with the previously described methods.

With water as the carrier medium the operator is concerned with, and limited by, the heat required to dissociate the water. With liquid fuel as a substitute for water in the slurry, the-operator need not be as concerned with the heat of dissociation problem because the carrier medium, to the extent liquid fuel is substituted for water, adds heat. The operator must still be concerned with the sensible heat required to bring the slurry up to blast furnace operating temperature and with the heat of dissociation of any Water in the slurry. Sensible heat is of concern with any fuel however, including coke added at the top of the furnace. Heating the blast gas and heating the fuel slurry can make up a great deal of the sensible heat requirements; an advantage not practicably available to the same extent with coke.

With liquid fuels, the net heat added to a blast furnace is positive, not so with water. Therefore liquid fuels can be substituted in part, or in whole, for water in the fuel slurry and the amount of slurry which can be added to a furnace is increased over that which the furnace could handle with water alone as the carrier medium. Liquid fuel, as used herein, is defined as any liquid hydrocarbon, or liquifiable hydrocarbon, including the low volatile and the high volatile oils, the low and high viscosity oils, and the low and high sulfur oils. The pulverized solid fuels, as covered earlier, include a broad range of fuels such as anthracite, bituminous, or strip coal, petroleum coke, char, common coke, or other carbonaceous solids. In the selection of solid fuels and oils, the range of sulfur contents in these fuels must be considered for its effect on the sulfur content of the metal.

Considering the blast furnace described earlier which operates at 2,000 tons of iron per day, with a 1,200 lb. coke rate, and 75,000 cu. ft. per minute of blast gas, if one-fourth by weight of the water in the two parts by Weight coal-on-e part by weight Water slurry is replaced with oil, the grains of moisture added to the furnace and the temperature required at various percentages of fuel slurry injection are shown in Table III.

TABLE #111 Pulverized solid fuel-water oil slurry Fuel Slurry Injee- Grains of Blast tion, Percent of Pulverized Oil, Moisture Gas Tem- Total Fuel Solid Fuel, lbs/day per cu. ft. perature Requirement lbs/day of Blast Required,

Gas F.

Increasing the percentage of oil substituted for water as a carrier medium increases the amount of fuel slurry which can be injected at a given blast temperature, and vice versa.

When oil is used as a carrier medium, a fuel in addition to the pulverized solid fuel is being added to the furnace; coke additions should be decreased in accordance with the amount of oil added. With pulverized coal, coke should be reduced by slightly over one pound for each pound of pulverized coal; with oil, coke should be reduced by about a pound, or slightly under one pound for each pound of oil. Limiting factors on the amount of fuel which can be injected when an oil carrier is used are the porosity requirements of the burden and the sensible heat required to bring the fuel slurry up to blast furnace operating temperature without cooling the furnace sufiiciently to throw off metal analysis.

Combining an oil carrier medium with oxygen enrichment further lowers the required blast gas temperature. Table IV shows the blast gas temperature required when oil is substituted for one-fourth by weight of the Water in a two parts by weight coal-one part by weight water slurry and the blast gas is enriched with oxygen.

In Tables I through IV the grains of moisture added per cu. ft. of blast gas do not take into account the grains of moisture in air due to ambient humidity at the blast furnace site. In summer, such moisture can average about 7 grains per cu. ft. of blast gas. To accommodate moisture due to ambient humidity, blast gas temperature can be increased about 30 F. for each grain per cu. ft. of moisture; where increases in blast temperature are not available, liquid fuel can be substituted for water in the slurry or oxygen enrichment can be increased, the amount of each being readily determined by interpolation of Tables I through IV.

In Tables II and IV, percentage oxygen enrichment refers to volumetric increase in the percentage of oxygen in the blast gas air.

The term fuel slurry, as used herein,refers to a slurry used primarily for introducing fuel comprising a pulverized solid carbonaceous material in a liquid carrier medium, but the term also refers to a slurry including pulverized solids in addition to pulverized solid carbonaceous material. For example, the fuel slurry may include flue dust, iron ore fines, iron ore concentrates, limestone fines, dolomite fines, etc. Injections of such pulverized materials can be used to control the blast furnace reaction and temperature, and metal analysis. More importantly, these materials can be added without sintering. Flue dust, for example, which is an excellent blast furnace additive because it is practically self-finxing, must ordinarily be agglomerated by sintering before it is added to a furnace. In accordance with the invention, fiue dust can be added as recovered from top gases without agglomeration and economic savings result. When additional fines are added with the fuel slurry, the sensible heat requirements of such fines must be considered. If needed, such heat requirements can be made up by increased blast temperature, substituting liquid fuel for water in the slurry, or oxygen enrichment.

Another economic advantage of the invention is obtaining increased production rate without a corresponding increase in required coking capacity. When adding pulverized coal slurry, for example, the coking operation takes place within the blast furnace and the volatile matter (coke oven gas) is used directly as a reductant.

Increasing the production rate of a blast furnace without increasing its size is another important economic advantage. The heat losses of the furnace remain about the same and can be distributed over a greater production thereby lowering the heat losses per ton of furnace production.

Various novel methods of introduction, novel blast furnace processes, and operational and economic advantages have been set forth dealing with supplanting top added blast furnace coke with a bottom added fuel slurry. In the light of the above disclosure, modification of such fuels and procedures can be made without departing from the spirit of the invention; therefore it is to be understood that the invention can be practiced otherwise than as specifically described above while remaining within the scope of the appended claim.

What is claimed is:

Method of operating an iron-producing blast furnace in which iron-bearing material, coke additions and slagforming material are introduced at the top of the blast furnace and combustion supporting blast gas is introduced at the bottom of the furnace comprising the steps of preheating the blast gas to a temperature in a range from approximately 1000 F. to approximately 2300 F., injecting a fuel slurry into the blast gas, the fuel slurry comprising a pulverized solid carbonaceous material in a carrier including water and a liquid fuel, enriching the blast gas with oxygen,

coordinating the blast temperature, fuel slurry injection, oxygen enrichment, and coke additions by increasing the blast temperature and oxygen enrichment when the rate of fuel slurry injection is increased to compensate for endothermic requirements of the fuel slurry injected and decreasing coke addi tions when the rate of fuel slurry injection is increased to compensate for the heat and reductants added by the fuel slurry.

References Cited by the Examiner UNITED STATES PATENTS 2,279,399 4/ 1942 Hogberg -41 2,824,792 2/1958 Rees 75-40 2,833,643 5/1958 Newman 75-41 2,938,782 5/1960 Toulmin 75-42 X 2,970,901 2/1961 Rice 75-41 2,980,416 4/1961 Strassburger 75-44 X 3,110,584 11/1963 Sanders 75-42 3,116,143 12/1963 Reichl 75-42 FOREIGN PATENTS 834,043 5/1960 Great Britain.

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner. 

